History-based motion vector predictor constraint for merge estimation region

ABSTRACT

A device for decoding video data can be configured to store a table of history-based motion vector predictors (HMVPs); determine motion information for a first block of the video data; add the motion information for the first block to the table of HMVPs in response to determining that the first block is located at a bottom-right corner of a motion estimation region (MER); and use the table of HMVPs to decode a second block of the video data.

This application claims the benefit of U.S. Provisional PatentApplication 62/955,977, filed 31 Dec. 2019, the entire content of eachbeing incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to video encoding and video decoding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), ITU-T H.265/High Efficiency Video Coding (HEVC), andextensions of such standards. The video devices may transmit, receive,encode, decode, and/or store digital video information more efficientlyby implementing such video coding techniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video picture or a portion of a video picture) maybe partitioned into video blocks, which may also be referred to ascoding tree units (CTUs), coding units (CUs) and/or coding nodes. Videoblocks in an intra-coded (I) slice of a picture are encoded usingspatial prediction with respect to reference samples in neighboringblocks in the same picture. Video blocks in an inter-coded (P or B)slice of a picture may use spatial prediction with respect to referencesamples in neighboring blocks in the same picture or temporal predictionwith respect to reference samples in other reference pictures. Picturesmay be referred to as frames, and reference pictures may be referred toas reference frames.

SUMMARY

A merge estimation region (MER) generally refers to a region of one ormore blocks, in which a video encoder and video decoder may derive mergecandidate lists for the blocks of the region in parallel. As will beexplained in greater detail below, existing implementations ofhistory-based motion vector predictors (HMVPs) may prevent theparallelization of merge candidate list derivation achieved using MERs.Thus, existing implementations of HMVP may not be able to be used inconjunction with MERs. This disclosure describes techniques formaintaining an HMVP table in a manner that may enable HMVP to be used inconjunction with MER. More specifically, by adding the motioninformation for a block to a table of HMVPs in response to determiningthat the first block is located at a bottom-right corner of a MER, avideo encoder and video decoder may be able to simultaneously implementHMVP while at the same time achieving the parallelization of MER.

According to one example, a method for decoding video data includesstoring a table of history-based motion vector predictors (HMVPs);determining motion information for a first block of the video data;adding the motion information for the first block to the table of HMVPsin response to determining that the first block is located at abottom-right corner of a motion estimation region (MER); and using thetable of HMVPs to decode a second block of the video data.

According to another example, a device for decoding video data includesa memory configured to store video data and one or more processorsimplemented in circuitry and configured to store a table ofhistory-based motion vector predictors (HMVPs); determine motioninformation for a first block of the video data; add the motioninformation for the first block to the table of HMVPs in response todetermining that the first block is located at a bottom-right corner ofa motion estimation region (MER); and use the table of HMVPs to decode asecond block of the video data.

According to another example, computer-readable storage medium storinginstructions that when executed by one or more processors cause the oneor more processors to store a table of history-based motion vectorpredictors (HMVPs); determine motion information for a first block ofthe video data; add the motion information for the first block to thetable of HMVPs in response to determining that the first block islocated at a bottom-right corner of a motion estimation region (MER);and use the table of HMVPs to decode a second block of the video data.

According to another example, an apparatus for decoding video dataincludes means for storing a table of history-based motion vectorpredictors (HMVPs); means for determining motion information for a firstblock of the video data; means for adding the motion information for thefirst block to the table of HMVPs in response to determining that thefirst block is located at a bottom-right corner of a motion estimationregion (MER); and means for using the table of HMVPs to decode a secondblock of the video data.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may perform the techniques of this disclosure.

FIGS. 2A and 2B are conceptual diagrams illustrating an example quadtreebinary tree (QTBT) structure, and a corresponding coding tree unit(CTU).

FIG. 3 is a conceptual diagram illustrating example merge estimationregions.

FIG. 4 is a block diagram illustrating an example video encoder that mayperform the techniques of this disclosure.

FIG. 5 is a block diagram illustrating an example video decoder that mayperform the techniques of this disclosure.

FIG. 6 is a flowchart illustrating an example video encoding process.

FIG. 7 is a flowchart illustrating an example video decoding process.

FIG. 8 is a flowchart illustrating an example video decoding process.

DETAILED DESCRIPTION

Video coding (e.g., video encoding and/or video decoding) typicallyinvolves predicting a block of video data from either an already codedblock of video data in the same picture (e.g., intra prediction) or analready coded block of video data in a different picture (e.g., interprediction). In some instances, the video encoder also calculatesresidual data by comparing the prediction block to the original block.Thus, the residual data represents a difference between the predictionblock and the original block. To reduce the number of bits needed tosignal the residual data, the video encoder transforms and quantizes theresidual data and signals the transformed and quantized residual data inthe encoded bitstream. The compression achieved by the transform andquantization processes may be lossy, meaning that transform andquantization processes may introduce distortion into the decoded videodata.

A video decoder decodes and adds the residual data to the predictionblock to produce a reconstructed video block that matches the originalvideo block more closely than the prediction block alone. Due to theloss introduced by the transforming and quantizing of the residual data,the first reconstructed block may have distortion or artifacts. Onecommon type of artifact or distortion is referred to as blockiness,where the boundaries of the blocks used to code the video data arevisible.

To further improve the quality of decoded video, a video decoder canperform one or more filtering operations on the reconstructed videoblocks. Examples of these filtering operations include deblockingfiltering, sample adaptive offset (SAO) filtering, and adaptive loopfiltering (ALF). Parameters for these filtering operations may either bedetermined by a video encoder and explicitly signaled in the encodedvideo bitstream or may be implicitly determined by a video decoderwithout needing the parameters to be explicitly signaled in the encodedvideo bitstream.

As will be described in more detail below, when coding a block of videodata using inter prediction, a video encoder and video decoder may beconfigured to code the block in various modes. One such mode is mergemode. In merge mode, a video encoder and video decoder are configured togenerate a list of merge candidates, where each merge candidate in thelist includes motion information for predicting a block. The motioninformation may, for example, include one or more motion vectors and oneor more reference picture identifies.

By implementing the same list generation process and only usingavailable information from already coded blocks, a video encoder andvideo decoder can be configured to generate the same lists with the samemerge candidates in the same order. Thus, for a video encoder to signalmotion information in merge mode, the video encoder can include in theencoded bitstream an index identifying one of the merge candidates. Asthe video decoder has constructed the same list as the video encoder,the video decoder can determine the motion information associated withthe merge candidate associated with the received index. In merge mode,the video decoder determines a predictive block based on the motioninformation associated with the merge candidate associated with thereceived index.

The video encoder and video decoder may generate the list of mergecandidates for a block by adding, in a pre-defined order, the motioninformation of spatially neighboring blocks in the same picture as theblock, co-located blocks in different pictures, artificially generatedcandidates, default candidates, or other such candidates. In someinstances, the video encoder and video decoder may also be configured toadd history-based candidates that include previously used motioninformation that may not correspond to spatially neighboring blocks orco-located blocks. To determine the history-based candidate, the videoencoder and video decoder may each maintain, e.g., store and update, ahistory-based motion vector prediction (HMVP) table. The video encoderand video decoder may store a predefined number of motion vectors in theHMVP table. As new motion vectors are added to the HMVP table, oldermotion vectors may be removed (e.g., in a first-in, first-out fashion).In some circumstances, the video encoder and video decoder may beconfigured to add the motion information of an entry from the HMVP tableto the list of merge candidates for a merge coded video block.

A video encoder and video decoder may also be configured to code blocksusing merge estimation regions (MERs) in a picture of video data. Avideo encoder and/or video decoder may be configured to perform a mergemode motion vector prediction process (e.g., motion vector predictorlist construction such as merge candidate list construction) in parallelfor a plurality of blocks (e.g., coding units) that are within a MER.

As will be explained in greater detail below, existing implementationsof HMVP may prevent the parallelization of merge candidate listderivation achieved using MERs. Thus, existing implementations of HMVPmay not be able to be used in conjunction with MERs. This disclosuredescribes techniques for maintaining an HMVP table in a manner that mayenable HMVP to be used in conjunction with MER. More specifically, byadding the motion information for a block to a table of HMVPs inresponse to determining that the first block is located at abottom-right corner of a motion estimation region, a video encoder andvideo decoder may be able to simultaneously implement both HMVP and MER.

As used in this disclosure, the term video coding generically refers toeither video encoding or video decoding. Similarly, the term video codermay generically refer to a video encoder or a video decoder. Moreover,certain techniques described in this disclosure with respect to videodecoding may also apply to video encoding, and vice versa. For example,often times video encoders and video decoders are configured to performthe same process, or reciprocal processes. For example, both a videoencoder and a video decoder may be configured to use the same rules forgenerating HMVP tables, such that both the video encoder and videodecoder can maintain the same HMVP tables without the need for anysignificant signaling overhead. Also, a video encoder typically performsvideo decoding (also called reconstruction) as part of the processes ofdetermining how to encode video data.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system 100 that may perform the techniques of this disclosure.The techniques of this disclosure are generally directed to coding(encoding and/or decoding) video data. In general, video data includesany data for processing a video. Thus, video data may include raw,unencoded video, encoded video, decoded (e.g., reconstructed) video, andvideo metadata, such as signaling data.

As shown in FIG. 1 , system 100 includes a source device 102 thatprovides encoded video data to be decoded and displayed by a destinationdevice 116, in this example. In particular, source device 102 providesthe video data to destination device 116 via a computer-readable medium110. Source device 102 and destination device 116 may comprise any of awide range of devices, including desktop computers, notebook (i.e.,laptop) computers, mobile devices, tablet computers, set-top boxes,telephone handsets such as smartphones, televisions, cameras, displaydevices, digital media players, video gaming consoles, video streamingdevice, broadcast receiver devices, or the like. In some cases, sourcedevice 102 and destination device 116 may be equipped for wirelesscommunication, and thus may be referred to as wireless communicationdevices.

In the example of FIG. 1 , source device 102 includes video source 104,memory 106, video encoder 200, and output interface 108. Destinationdevice 116 includes input interface 122, video decoder 300, memory 120,and display device 118. In accordance with this disclosure, videoencoder 200 of source device 102 and video decoder 300 of destinationdevice 116 may be configured to apply the techniques for updating HMVPtables disclosed herein. Thus, source device 102 represents an exampleof a video encoding device, while destination device 116 represents anexample of a video decoding device. In other examples, a source deviceand a destination device may include other components or arrangements.For example, source device 102 may receive video data from an externalvideo source, such as an external camera. Likewise, destination device116 may interface with an external display device, rather than includean integrated display device.

System 100 as shown in FIG. 1 is merely one example. In general, anydigital video encoding and/or decoding device may perform techniques forupdating HMVP tables disclosed herein. Source device 102 and destinationdevice 116 are merely examples of such coding devices in which sourcedevice 102 generates coded video data for transmission to destinationdevice 116. This disclosure refers to a “coding” device as a device thatperforms coding (encoding and/or decoding) of data. Thus, video encoder200 and video decoder 300 represent examples of coding devices, inparticular, a video encoder and a video decoder, respectively. In someexamples, source device 102 and destination device 116 may operate in asubstantially symmetrical manner such that each of source device 102 anddestination device 116 includes video encoding and decoding components.Hence, system 100 may support one-way or two-way video transmissionbetween source device 102 and destination device 116, e.g., for videostreaming, video playback, video broadcasting, or video telephony.

In general, video source 104 represents a source of video data (i.e.,raw, unencoded video data) and provides a sequential series of pictures(also referred to as “frames”) of the video data to video encoder 200,which encodes data for the pictures. Video source 104 of source device102 may include a video capture device, such as a video camera, a videoarchive containing previously captured raw video, and/or a video feedinterface to receive video from a video content provider. As a furtheralternative, video source 104 may generate computer graphics-based dataas the source video, or a combination of live video, archived video, andcomputer-generated video. In each case, video encoder 200 encodes thecaptured, pre-captured, or computer-generated video data. Video encoder200 may rearrange the pictures from the received order (sometimesreferred to as “display order”) into a coding order for coding. Videoencoder 200 may generate a bitstream including encoded video data.Source device 102 may then output the encoded video data via outputinterface 108 onto computer-readable medium 110 for reception and/orretrieval by, e.g., input interface 122 of destination device 116.

Memory 106 of source device 102 and memory 120 of destination device 116represent general purpose memories. In some examples, memories 106, 120may store raw video data, e.g., raw video from video source 104 and raw,decoded video data from video decoder 300. Additionally oralternatively, memories 106, 120 may store software instructionsexecutable by, e.g., video encoder 200 and video decoder 300,respectively. Although memory 106 and memory 120 are shown separatelyfrom video encoder 200 and video decoder 300 in this example, it shouldbe understood that video encoder 200 and video decoder 300 may alsoinclude internal memories for functionally similar or equivalentpurposes. Furthermore, memories 106, 120 may store encoded video data,e.g., output from video encoder 200 and input to video decoder 300. Insome examples, portions of memories 106, 120 may be allocated as one ormore video buffers, e.g., to store raw, decoded, and/or encoded videodata.

Computer-readable medium 110 may represent any type of medium or devicecapable of transporting the encoded video data from source device 102 todestination device 116. In one example, computer-readable medium 110represents a communication medium to enable source device 102 totransmit encoded video data directly to destination device 116 inreal-time, e.g., via a radio frequency network or computer-basednetwork. Output interface 108 may modulate a transmission signalincluding the encoded video data, and input interface 122 may demodulatethe received transmission signal, according to a communication standard,such as a wireless communication protocol. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from source device 102 to destination device 116.

In some examples, source device 102 may output encoded data from outputinterface 108 to storage device 112. Similarly, destination device 116may access encoded data from storage device 112 via input interface 122.Storage device 112 may include any of a variety of distributed orlocally accessed data storage media such as a hard drive, Blu-ray discs,DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or anyother suitable digital storage media for storing encoded video data.

In some examples, source device 102 may output encoded video data tofile server 114 or another intermediate storage device that may storethe encoded video data generated by source device 102. Destinationdevice 116 may access stored video data from file server 114 viastreaming or download.

File server 114 may be any type of server device capable of storingencoded video data and transmitting that encoded video data to thedestination device 116. File server 114 may represent a web server(e.g., for a website), a server configured to provide a file transferprotocol service (such as File Transfer Protocol (FTP) or File Deliveryover Unidirectional Transport (FLUTE) protocol), a content deliverynetwork (CDN) device, a hypertext transfer protocol (HTTP) server, aMultimedia Broadcast Multicast Service (MBMS) or Enhanced MBMS (eMBMS)server, and/or a network attached storage (NAS) device. File server 114may, additionally or alternatively, implement one or more HTTP streamingprotocols, such as Dynamic Adaptive Streaming over HTTP (DASH), HTTPLive Streaming (HLS), Real Time Streaming Protocol (RTSP), HTTP DynamicStreaming, or the like.

Destination device 116 may access encoded video data from file server114 through any standard data connection, including an Internetconnection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., digital subscriber line (DSL),cable modem, etc.), or a combination of both that is suitable foraccessing encoded video data stored on file server 114. Input interface122 may be configured to operate according to any one or more of thevarious protocols discussed above for retrieving or receiving media datafrom file server 114, or other such protocols for retrieving media data.

Output interface 108 and input interface 122 may represent wirelesstransmitters/receivers, modems, wired networking components (e.g.,Ethernet cards), wireless communication components that operateaccording to any of a variety of IEEE 802.11 standards, or otherphysical components. In examples where output interface 108 and inputinterface 122 comprise wireless components, output interface 108 andinput interface 122 may be configured to transfer data, such as encodedvideo data, according to a cellular communication standard, such as 4G,4G-LTE (Long-Term Evolution), LTE Advanced, 5G, or the like. In someexamples where output interface 108 comprises a wireless transmitter,output interface 108 and input interface 122 may be configured totransfer data, such as encoded video data, according to other wirelessstandards, such as an IEEE 802.11 specification, an IEEE 802.15specification (e.g., ZigBee™), a Bluetooth™ standard, or the like. Insome examples, source device 102 and/or destination device 116 mayinclude respective system-on-a-chip (SoC) devices. For example, sourcedevice 102 may include an SoC device to perform the functionalityattributed to video encoder 200 and/or output interface 108, anddestination device 116 may include an SoC device to perform thefunctionality attributed to video decoder 300 and/or input interface122.

The techniques of this disclosure may be applied to video coding insupport of any of a variety of multimedia applications, such asover-the-air television broadcasts, cable television transmissions,satellite television transmissions, Internet streaming videotransmissions, such as dynamic adaptive streaming over HTTP (DASH),digital video that is encoded onto a data storage medium, decoding ofdigital video stored on a data storage medium, or other applications.

Input interface 122 of destination device 116 receives an encoded videobitstream from computer-readable medium 110 (e.g., a communicationmedium, storage device 112, file server 114, or the like). The encodedvideo bitstream may include signaling information defined by videoencoder 200, which is also used by video decoder 300, such as syntaxelements having values that describe characteristics and/or processingof video blocks or other coded units (e.g., slices, pictures, groups ofpictures, sequences, or the like). Display device 118 displays decodedpictures of the decoded video data to a user. Display device 118 mayrepresent any of a variety of display devices such as a liquid crystaldisplay (LCD), a plasma display, an organic light emitting diode (OLED)display, or another type of display device.

Although not shown in FIG. 1 , in some examples, video encoder 200 andvideo decoder 300 may each be integrated with an audio encoder and/oraudio decoder, and may include appropriate MUX-DEMUX units, or otherhardware and/or software, to handle multiplexed streams including bothaudio and video in a common data stream. If applicable, MUX-DEMUX unitsmay conform to the ITU H.223 multiplexer protocol, or other protocolssuch as the user datagram protocol (UDP).

Video encoder 200 and video decoder 300 each may be implemented as anyof a variety of suitable encoder and/or decoder circuitry, such as oneor more microprocessors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs), discrete logic, software, hardware, firmware or anycombinations thereof. When the techniques are implemented partially insoftware, a device may store instructions for the software in asuitable, non-transitory computer-readable medium and execute theinstructions in hardware using one or more processors to perform thetechniques of this disclosure. Each of video encoder 200 and videodecoder 300 may be included in one or more encoders or decoders, eitherof which may be integrated as part of a combined encoder/decoder (CODEC)in a respective device. A device including video encoder 200 and/orvideo decoder 300 may comprise an integrated circuit, a microprocessor,and/or a wireless communication device, such as a cellular telephone.

Video encoder 200 and video decoder 300 may operate according to a videocoding standard, such as ITU-T H.265, also referred to as HighEfficiency Video Coding (HEVC) or extensions thereto, such as themulti-view and/or scalable video coding extensions. Video encoder 200and video decoder 300 may additionally or alternatively operateaccording to other proprietary or industry standards, such as the JointExploration Test Model (JEM) or ITU-T H.266, also referred to asVersatile Video Coding (VVC). A recent draft of the VVC standard isdescribed in Bross, et al. “Versatile Video Coding (Draft 7),” JointVideo Experts Team (JVET) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG11, 16^(th) Meeting: Geneva, CH, 1-11 Oct. 2019, JVET-P2001-v14(hereinafter “VVC Draft 7”). Another draft of the VVC standard isdescribed in Bross, et al. “Versatile Video Coding (Draft 10),” JointVideo Experts Team (JVET) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG11, 18^(th) Meeting: by teleconference, 22 Jun.-1 Jul. 2020,JVET-52001-v17 (hereinafter “VVC Draft 10”). The techniques of thisdisclosure, however, are not limited to any particular coding standard.

In general, video encoder 200 and video decoder 300 may performblock-based coding of pictures. The term “block” generally refers to astructure including data to be processed (e.g., encoded, decoded, orotherwise used in the encoding and/or decoding process). For example, ablock may include a two-dimensional matrix of samples of luminanceand/or chrominance data. In general, video encoder 200 and video decoder300 may code video data represented in a YUV (e.g., Y, Cb, Cr) format.That is, rather than coding red, green, and blue (RGB) data for samplesof a picture, video encoder 200 and video decoder 300 may code luminanceand chrominance components, where the chrominance components may includeboth red hue and blue hue chrominance components. In some examples,video encoder 200 converts received RGB formatted data to a YUVrepresentation prior to encoding, and video decoder 300 converts the YUVrepresentation to the RGB format. Alternatively, pre- andpost-processing units (not shown) may perform these conversions.

This disclosure may generally refer to coding (e.g., encoding anddecoding) of pictures to include the process of encoding or decodingdata of the picture. Similarly, this disclosure may refer to coding ofblocks of a picture to include the process of encoding or decoding datafor the blocks, e.g., prediction and/or residual coding. An encodedvideo bitstream generally includes a series of values for syntaxelements representative of coding decisions (e.g., coding modes) andpartitioning of pictures into blocks. Thus, references to coding apicture or a block should generally be understood as coding values forsyntax elements forming the picture or block.

HEVC defines various blocks, including coding units (CUs), predictionunits (PUs), and transform units (TUs). According to HEVC, a video coder(such as video encoder 200) partitions a coding tree unit (CTU) into CUsaccording to a quadtree structure. That is, the video coder partitionsCTUs and CUs into four equal, non-overlapping squares, and each node ofthe quadtree has either zero or four child nodes. Nodes without childnodes may be referred to as “leaf nodes,” and CUs of such leaf nodes mayinclude one or more PUs and/or one or more TUs. The video coder mayfurther partition PUs and TUs. For example, in HEVC, a residual quadtree(RQT) represents partitioning of TUs. In HEVC, PUs representinter-prediction data, while TUs represent residual data. CUs that areintra-predicted include intra-prediction information, such as anintra-mode indication.

As another example, video encoder 200 and video decoder 300 may beconfigured to operate according to VVC. According to VVC, a video coder(such as video encoder 200) partitions a picture into a plurality ofcoding tree units (CTUs). Video encoder 200 may partition a CTUaccording to a tree structure, such as a quadtree-binary tree (QTBT)structure or Multi-Type Tree (MTT) structure. The QTBT structure removesthe concepts of multiple partition types, such as the separation betweenCUs, PUs, and TUs of HEVC. A QTBT structure includes two levels: a firstlevel partitioned according to quadtree partitioning, and a second levelpartitioned according to binary tree partitioning. A root node of theQTBT structure corresponds to a CTU. Leaf nodes of the binary treescorrespond to coding units (CUs).

In an MTT partitioning structure, blocks may be partitioned using aquadtree (QT) partition, a binary tree (BT) partition, and one or moretypes of triple tree (TT) (also called ternary tree (TT)) partitions. Atriple or ternary tree partition is a partition where a block is splitinto three sub-blocks. In some examples, a triple or ternary treepartition divides a block into three sub-blocks without dividing theoriginal block through the center. The partitioning types in MTT (e.g.,QT, BT, and TT), may be symmetrical or asymmetrical.

In some examples, video encoder 200 and video decoder 300 may use asingle QTBT or MTT structure to represent each of the luminance andchrominance components, while in other examples, video encoder 200 andvideo decoder 300 may use two or more QTBT or MTT structures, such asone QTBT/MTT structure for the luminance component and another QTBT/MTTstructure for both chrominance components (or two QTBT/MTT structuresfor respective chrominance components).

Video encoder 200 and video decoder 300 may be configured to usequadtree partitioning per HEVC, QTBT partitioning, MTT partitioning, orother partitioning structures. For purposes of explanation, thedescription of the techniques of this disclosure is presented withrespect to QTBT partitioning. However, it should be understood that thetechniques of this disclosure may also be applied to video codersconfigured to use quadtree partitioning, or other types of partitioningas well.

In some examples, a CTU includes a coding tree block (CTB) of lumasamples, two corresponding CTBs of chroma samples of a picture that hasthree sample arrays, or a CTB of samples of a monochrome picture or apicture that is coded using three separate color planes and syntaxstructures used to code the samples. A CTB may be an N×N block ofsamples for some value of N such that the division of a component intoCTBs is a partitioning. A component is an array or single sample fromone of the three arrays (luma and two chroma) that compose a picture in4:2:0, 4:2:2, or 4:4:4 color format or the array or a single sample ofthe array that compose a picture in monochrome format. In some examples,a coding block is an M×N block of samples for some values of M and Nsuch that a division of a CTB into coding blocks is a partitioning.

The blocks (e.g., CTUs or CUs) may be grouped in various ways in apicture. As one example, a brick may refer to a rectangular region ofCTU rows within a particular tile in a picture. A tile may be arectangular region of CTUs within a particular tile column and aparticular tile row in a picture. A tile column refers to a rectangularregion of CTUs having a height equal to the height of the picture and awidth specified by syntax elements (e.g., such as in a picture parameterset). A tile row refers to a rectangular region of CTUs having a heightspecified by syntax elements (e.g., such as in a picture parameter set)and a width equal to the width of the picture.

In some examples, a tile may be partitioned into multiple bricks, eachof which may include one or more CTU rows within the tile. A tile thatis not partitioned into multiple bricks may also be referred to as abrick. However, a brick that is a true subset of a tile may not bereferred to as a tile.

The bricks in a picture may also be arranged in a slice. A slice may bean integer number of bricks of a picture that may be exclusivelycontained in a single network abstraction layer (NAL) unit. In someexamples, a slice includes either a number of complete tiles or only aconsecutive sequence of complete bricks of one tile.

This disclosure may use “N×N” and “N by N” interchangeably to refer tothe sample dimensions of a block (such as a CU or other video block) interms of vertical and horizontal dimensions, e.g., 16×16 samples or 16by 16 samples. In general, a 16×16 CU will have 16 samples in a verticaldirection (y=16) and 16 samples in a horizontal direction (x=16).Likewise, an N×N CU generally has N samples in a vertical direction andN samples in a horizontal direction, where N represents a nonnegativeinteger value. The samples in a CU may be arranged in rows and columns.Moreover, CUs need not necessarily have the same number of samples inthe horizontal direction as in the vertical direction. For example, CUsmay comprise N×M samples, where M is not necessarily equal to N.

Video encoder 200 encodes video data for CUs representing predictionand/or residual information, and other information. The predictioninformation indicates how the CU is to be predicted in order to form aprediction block for the CU. The residual information generallyrepresents sample-by-sample differences between samples of the CU priorto encoding and the prediction block.

To predict a CU, video encoder 200 may generally form a prediction blockfor the CU through inter-prediction or intra-prediction.Inter-prediction generally refers to predicting the CU from data of apreviously coded picture, whereas intra-prediction generally refers topredicting the CU from previously coded data of the same picture. Toperform inter-prediction, video encoder 200 may generate the predictionblock using one or more motion vectors. Video encoder 200 may generallyperform a motion search to identify a reference block that closelymatches the CU, e.g., in terms of differences between the CU and thereference block. Video encoder 200 may calculate a difference metricusing a sum of absolute difference (SAD), sum of squared differences(SSD), mean absolute difference (MAD), mean squared differences (MSD),or other such difference calculations to determine whether a referenceblock closely matches the current CU. In some examples, video encoder200 may predict the current CU using uni-directional prediction orbi-directional prediction.

Video encoder 200 may signal motion parameters of a block in variousways. Such motion parameters may include motion vectors, referenceindexes, reference picture list indicators, and/or other data related tomotion. In some examples, video encoder 200 and video decoder 300 mayuse motion prediction to reduce the amount of data used for signalingmotion parameters. Motion prediction may comprise the determination ofmotion parameters of a block (e.g., a PU, a CU, etc.) based on motionparameters of one or more other blocks. There are various types ofmotion prediction. For instance, merge mode and advanced motion vectorprediction (AMVP) mode are two types of motion prediction.

In merge mode, video encoder 200 generates a candidate list. Thecandidate list includes a set of candidates that indicate the motionparameters of one or more source blocks. The source blocks may spatiallyor temporally neighbor a current block. Furthermore, in merge mode,video encoder 200 may select a candidate from the candidate list and mayuse the motion parameters indicated by the selected candidate as themotion parameters of the current block. Video encoder 200 may signal theposition in the candidate list of the selected candidate. Video decoder300 may determine, based on information obtained from a bitstream, theindex into the candidate list. In addition, video decoder 300 maygenerate the same candidate list and may determine, based on the index,the selected candidate. Video decoder 300 may then use the motionparameters of the selected candidate to generate a predictor block forthe current block.

Skip mode is similar to merge mode. In skip mode, video encoder 200 andvideo decoder 300 generate and use a candidate list in the same way thatvideo encoder 200 and video decoder 300 use the candidate list in mergemode. However, when video encoder 200 signals the motion parameters of acurrent block using skip mode, video encoder 200 does not signal anyresidual data for the current block. Accordingly, video decoder 300 maydetermine a predictor block for the current block based on one or morereference blocks indicated by the motion parameters of a selectedcandidate in the candidate list. Video decoder 300 may then reconstructsamples in a coding block of the current block such that thereconstructed samples are equal to corresponding samples in thepredictor block of the current block.

AMVP mode is similar to merge mode in that video encoder 200 maygenerate a candidate list for a current block and may select a candidatefrom the candidate list. However, for each respective reference blockused in determining a predictor block for the current block, videoencoder 200 may signal a respective motion vector difference (MVD) forthe current block, a respective reference index for the current block,and a respective candidate index indicating a selected candidate in thecandidate list. An MVD for a block may indicate a difference between amotion vector of the block and a motion vector of the selectedcandidate. The reference index for the current block indicates areference picture from which a reference block is determined.

Furthermore, when AMVP mode is used, for each respective reference blockused in determining a predictor block for the current block, videodecoder 300 may determine an MVD for the current block, a referenceindex for the current block, and a candidate index and a motion vectorprediction (MVP) flag. Video decoder 300 may generate the same candidatelist and may determine, based on the candidate index, a selectedcandidate in the candidate list. As before, this candidate list mayinclude motion vectors of neighboring blocks that are associated withthe same reference index as well as a temporal motion vector predictorwhich is derived based on the motion parameters of the neighboring blockof the co-located block in a temporal reference picture. Video decoder300 may recover a motion vector of the current block by adding the MVDto the motion vector indicated by the selected AMVP candidate. That is,video decoder 300 may determine, based on a motion vector indicated bythe selected AMVP candidate and the MVD, the motion vector of thecurrent block. Video decoder 300 may then use the recovered motionvector or motion vectors of the current block to generate predictorblocks for the current block.

When a video coder (e.g., video encoder 200 or video decoder 300)generates an AMVP candidate list for a current block, the video codermay derive one or more AMVP candidates based on the motion parameters ofreference blocks (e.g., spatially-neighboring blocks) that containlocations that spatially neighbor the current PU and one or more AMVPcandidates based on motion parameters of PUs that temporally neighborthe current PU. The candidate list may include motion vectors ofreference blocks that are associated with the same reference index aswell as a temporal motion vector predictor which is derived based on themotion parameters (i.e., motion parameters) of the neighboring block ofthe co-located block in a temporal reference picture. A candidate in amerge candidate list or an AMVP candidate list that is based on themotion parameters of a reference block that temporally neighbors acurrent block. This disclosure may use the term “temporal motion vectorpredictor” to refer to a block that is in a different time instance thanthe current block and is used for motion vector prediction.

Some examples of VVC also provide an affine motion compensation mode,which may be considered an inter-prediction mode. In affine motioncompensation mode, video encoder 200 may determine two or more motionvectors that represent non-translational motion, such as zoom in or out,rotation, perspective motion, or other irregular motion types.

To perform intra-prediction, video encoder 200 may select anintra-prediction mode to generate the prediction block. Some examples ofVVC provide sixty-seven intra-prediction modes, including variousdirectional modes, as well as planar mode and DC mode. In general, videoencoder 200 selects an intra-prediction mode that describes neighboringsamples to a current block (e.g., a block of a CU) from which to predictsamples of the current block. Such samples may generally be above, aboveand to the left, or to the left of the current block in the same pictureas the current block, assuming video encoder 200 codes CTUs and CUs inraster scan order (left to right, top to bottom).

Video encoder 200 encodes data representing the prediction mode for acurrent block. For example, for inter-prediction modes, video encoder200 may encode data representing which of the various availableinter-prediction modes is used, as well as motion information for thecorresponding mode. For uni-directional or bi-directionalinter-prediction, for example, video encoder 200 may encode motionvectors using AMVP or merge mode. Video encoder 200 may use similarmodes to encode motion vectors for affine motion compensation mode.

Following prediction, such as intra-prediction or inter-prediction of ablock, video encoder 200 may calculate residual data for the block. Theresidual data, such as a residual block, represents sample by sampledifferences between the block and a prediction block for the block,formed using the corresponding prediction mode. Video encoder 200 mayapply one or more transforms to the residual block, to producetransformed data in a transform domain instead of the sample domain. Forexample, video encoder 200 may apply a discrete cosine transform (DCT),an integer transform, a wavelet transform, or a conceptually similartransform to residual video data. Additionally, video encoder 200 mayapply a secondary transform following the first transform, such as amode-dependent non-separable secondary transform (MDNSST), a signaldependent transform, a Karhunen-Loeve transform (KLT), or the like.Video encoder 200 produces transform coefficients following applicationof the one or more transforms.

As noted above, following any transforms to produce transformcoefficients, video encoder 200 may perform quantization of thetransform coefficients. Quantization generally refers to a process inwhich transform coefficients are quantized to possibly reduce the amountof data used to represent the transform coefficients, providing furthercompression. By performing the quantization process, video encoder 200may reduce the bit depth associated with some or all of the transformcoefficients. For example, video encoder 200 may round an n-bit valuedown to an m-bit value during quantization, where n is greater than m.In some examples, to perform quantization, video encoder 200 may performa bitwise right-shift of the value to be quantized.

Following quantization, video encoder 200 may scan the transformcoefficients, producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) transform coefficients at the front of the vector and toplace lower energy (and therefore higher frequency) transformcoefficients at the back of the vector. In some examples, video encoder200 may utilize a predefined scan order to scan the quantized transformcoefficients to produce a serialized vector, and then entropy encode thequantized transform coefficients of the vector. In other examples, videoencoder 200 may perform an adaptive scan. After scanning the quantizedtransform coefficients to form the one-dimensional vector, video encoder200 may entropy encode the one-dimensional vector, e.g., according tocontext-adaptive binary arithmetic coding (CABAC). Video encoder 200 mayalso entropy encode values for syntax elements describing metadataassociated with the encoded video data for use by video decoder 300 indecoding the video data.

To perform CABAC, video encoder 200 may assign a context within acontext model to a symbol to be transmitted. The context may relate to,for example, whether neighboring values of the symbol are zero-valued ornot. The probability determination may be based on a context assigned tothe symbol.

Video encoder 200 may further generate syntax data, such as block-basedsyntax data, picture-based syntax data, and sequence-based syntax data,to video decoder 300, e.g., in a picture header, a block header, a sliceheader, or other syntax data, such as a sequence parameter set (SPS),picture parameter set (PPS), or video parameter set (VPS). Video decoder300 may likewise decode such syntax data to determine how to decodecorresponding video data.

In this manner, video encoder 200 may generate a bitstream includingencoded video data, e.g., syntax elements describing partitioning of apicture into blocks (e.g., CUs) and prediction and/or residualinformation for the blocks. Ultimately, video decoder 300 may receivethe bitstream and decode the encoded video data.

In general, video decoder 300 performs a reciprocal process to thatperformed by video encoder 200 to decode the encoded video data of thebitstream. For example, video decoder 300 may decode values for syntaxelements of the bitstream using CABAC in a manner substantially similarto, albeit reciprocal to, the CABAC encoding process of video encoder200. The syntax elements may define partitioning information forpartitioning of a picture into CTUs, and partitioning of each CTUaccording to a corresponding partition structure, such as a QTBTstructure, to define CUs of the CTU. The syntax elements may furtherdefine prediction and residual information for blocks (e.g., CUs) ofvideo data.

The residual information may be represented by, for example, quantizedtransform coefficients. Video decoder 300 may inverse quantize andinverse transform the quantized transform coefficients of a block toreproduce a residual block for the block. Video decoder 300 uses asignaled prediction mode (intra- or inter-prediction) and relatedprediction information (e.g., motion information for inter-prediction)to form a prediction block for the block. Video decoder 300 may thencombine the prediction block and the residual block (on asample-by-sample basis) to reproduce the original block. Video decoder300 may perform additional processing, such as performing a deblockingprocess to reduce visual artifacts along boundaries of the block.

This disclosure may generally refer to “signaling” certain information,such as syntax elements. The term “signaling” may generally refer to thecommunication of values for syntax elements and/or other data used todecode encoded video data. That is, video encoder 200 may signal valuesfor syntax elements in the bitstream. In general, signaling refers togenerating a value in the bitstream. As noted above, source device 102may transport the bitstream to destination device 116 substantially inreal time, or not in real time, such as might occur when storing syntaxelements to storage device 112 for later retrieval by destination device116.

FIGS. 2A and 2B are conceptual diagrams illustrating an example quadtreebinary tree (QTBT) structure 130, and a corresponding coding tree unit(CTU) 132. The solid lines represent quadtree splitting, and dottedlines indicate binary tree splitting. In each split (i.e., non-leaf)node of the binary tree, one flag is signaled to indicate whichsplitting type (i.e., horizontal or vertical) is used, where 0 indicateshorizontal splitting and 1 indicates vertical splitting in this example.For the quadtree splitting, there is no need to indicate the splittingtype, because quadtree nodes split a block horizontally and verticallyinto 4 sub-blocks with equal size. Accordingly, video encoder 200 mayencode, and video decoder 300 may decode, syntax elements (such assplitting information) for a region tree level of QTBT structure 130(i.e., the solid lines) and syntax elements (such as splittinginformation) for a prediction tree level of QTBT structure 130 (i.e.,the dashed lines). Video encoder 200 may encode, and video decoder 300may decode, video data, such as prediction and transform data, for CUsrepresented by terminal leaf nodes of QTBT structure 130.

In general, CTU 132 of FIG. 2B may be associated with parametersdefining sizes of blocks corresponding to nodes of QTBT structure 130 atthe first and second levels. These parameters may include a CTU size(representing a size of CTU 132 in samples), a minimum quadtree size(MinQTSize, representing a minimum allowed quadtree leaf node size), amaximum binary tree size (MaxBTSize, representing a maximum allowedbinary tree root node size), a maximum binary tree depth (MaxBTDepth,representing a maximum allowed binary tree depth), and a minimum binarytree size (MinBTSize, representing the minimum allowed binary tree leafnode size).

The root node of a QTBT structure corresponding to a CTU may have fourchild nodes at the first level of the QTBT structure, each of which maybe partitioned according to quadtree partitioning. That is, nodes of thefirst level are either leaf nodes (having no child nodes) or have fourchild nodes. The example of QTBT structure 130 represents such nodes asincluding the parent node and child nodes having solid lines forbranches. If nodes of the first level are not larger than the maximumallowed binary tree root node size (MaxBTSize), then the nodes can befurther partitioned by respective binary trees. The binary treesplitting of one node can be iterated until the nodes resulting from thesplit reach the minimum allowed binary tree leaf node size (MinBTSize)or the maximum allowed binary tree depth (MaxBTDepth). The example ofQTBT structure 130 represents such nodes as having dashed lines forbranches. The binary tree leaf node is referred to as a coding unit(CU), which is used for prediction (e.g., intra-picture or inter-pictureprediction) and transform, without any further partitioning. Asdiscussed above, CUs may also be referred to as “video blocks” or“blocks.”

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 (luma samples and two corresponding 64×64 chroma samples),the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64, theMinBTSize (for both width and height) is set as 4, and the MaxBTDepth isset as 4. The quadtree partitioning is applied to the CTU first togenerate quad-tree leaf nodes. The quadtree leaf nodes may have a sizefrom 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If thequadtree leaf node is 128×128, the leaf quadtree node will not befurther split by the binary tree, because the size exceeds the MaxBTSize(i.e., 64×64, in this example). Otherwise, the quadtree leaf node willbe further partitioned by the binary tree. Therefore, the quadtree leafnode is also the root node for the binary tree and has the binary treedepth as 0. When the binary tree depth reaches MaxBTDepth (4, in thisexample), no further splitting is permitted. A binary tree node having awidth equal to MinBTSize (4, in this example) implies that no furthervertical splitting (that is, dividing of the width) is permitted forthat binary tree node. Similarly, a binary tree node having a heightequal to MinBTSize implies no further horizontal splitting (that is,dividing of the height) is permitted for that binary tree node. As notedabove, leaf nodes of the binary tree are referred to as CUs, and arefurther processed according to prediction and transform without furtherpartitioning.

As introduced above, video encoder 200 and video decoder 300 may beconfigured to code blocks of video data in a merge mode, which is a modefor signaling inter-prediction motion information. The merge candidatelist construction process in some example video codecs (e.g., HEVC andVVC) may introduce dependencies between neighboring blocks due to theuse of spatial merge candidates. In some example video encoderimplementations, the motion estimation stage (e.g., the motionestimation performed by motion estimation unit 222 of FIG. 3 ) forneighboring blocks is typically performed in parallel or at leastpipelined to increase the throughput. Due to the dependency betweenneighboring blocks, merge candidate lists of neighboring blocks cannotbe generated in parallel and may represent a bottleneck for parallelencoder/decoder designs.

Therefore, a parallel merge estimation process was introduced in HEVC.The parallel merge estimation process in HEVC uses an indication of aregion (e.g., a MER) in which video encoder 200 and video decoder 300may derive merge candidate lists for two or more blocks at the sametime. Video encoder 200 and video decoder 300 may derive merge candidatelists for all blocks within a MER in parallel. In some examples, a MERmay include a single block. That is, video encoder 200 (e.g., via motionestimation unit 222 and motion compensation unit 224) and video decoder300 (e.g., via motion compensation unit 316) may perform a mergecandidate list construction process in parallel for multiple blockswithin the indicated region (e.g., the MER).

Video encoder 200 and video decoder 300 may determine blocks for whichto perform the parallel merge candidate list construction process bychecking whether a candidate block is inside the indicated MER. Acandidate block that is in the same MER as the current block is notincluded in the merge candidate list. Hence, the motion data of such acandidate does not need to be available at the time of the mergecandidate list construction.

In examples where the size of the MER is 32×32 samples, video encoder200 and video decoder 300 may be configured to construct the mergecandidate lists in parallel for all blocks (e.g., coding units orprediction units) in a 32×32 sample area, since all merge candidatesthat are within the same 32×32 MER are not added in the merge candidatelist. FIG. 3 illustrates an example partitioning of CTU 150 into sevenCUs and ten PUs. A first CU includes PU0 and PU1, a second CU includesPU2, a third CU includes PU3, a fourth CU includes PU4, a fifth CUincludes PU5 and PU6, a sixth CU includes PU7, and a seventh CU includesPU8 and PU9. In FIG. 3 , CTU 150 includes a 64×64 luma coding treeblock. Motion estimation for PUs inside 32×32 MERs 152 (dashed blocks)are carried out independently, enabling the performance of motionestimation (e.g., including merge candidate list construction) inparallel for PUs within each MER 152. For purposes of explanation, FIG.3 shows possible spatial merge candidates for PU0, PU5, and PU9.

In the example of FIG. 3 , merge candidates 154 for PU0 are availablefor use in a merge candidate list because those merge candidates areoutside the 32×32 MER that includes PU0. For the 32×32 MER thatencompasses PU2-PU6, the merge candidate lists of PU2-PU6 cannot includemotion data from any of PU2-PU6 because the merge estimation and mergecandidate list construction inside that MER should be independent (e.g.,will be performed in parallel). Therefore, with reference to PU5, mergecandidates 156 are unavailable because merge candidates 156 are in thesame MER that encompasses PU5. Merge candidate 158 for PU5 isunavailable because that candidate location has not yet been coded.Accordingly, the merge list of PU5 may only include a temporal candidate(if available) and zero MV candidates. For PU9, merge candidates 154 areavailable because those merge candidates are outside the MER thatencompasses PU9. Merge candidate 156 is unavailable because mergecandidate 156 is in the same MER as PU9, and merge candidates 158 arenot available because those candidate locations have not yet been coded.

In order to enable an encoder (e.g., video encoder 200) to trade-offparallelism and coding efficiency, the parallel merge estimation level(e.g., the size of the MER) may be adaptive and signaled using a syntaxelement. For example, video encoder 200 may signal a syntax element(e.g., log 2_parallel_merge_level_minus2) that indicates the size of theMER in a picture parameter set (PPS). The following MER sizes areallowed in HEVC: 4×4 (no parallel merge list construction possible),8×8, 16×16, 32×32 and 64×64. A higher degree of parallelization, enabledby a larger MER, excludes more potential candidates from the mergecandidate list. However, a larger MER may decrease coding efficiency.

HMVP in VVC Draft 7 prevents the parallelization of merge candidate listderivation. The HMVP merge candidates are added to the merge list afterthe spatial MVP and TMVP. In HMVP as implemented in VVC Draft 7, themotion information of a previously coded block is stored in a table andused as an MVP for the current CU. The table with multiple HMVPcandidates is maintained during the encoding/decoding process. The tableis reset (emptied) when a new CTU row is encountered. Whenever there isa non-subblock inter-coded CU, the associated motion information isadded to the last entry of the table as a new HMVP candidate. For blocksbeing coded in parallel within a MER, however, the motion information ofa previously coded block may not be known, thus resulting in either aninability to use HMVP or in a reduction of the parallelism achieved by aMER.

This disclosure describes processes for constraining the addition ofHMVP candidates to the table of HMVPs when using MER, such that bothHMVPs and MERs can be used in conjunction with one another. According toone technique of this disclosure, the updating of an HMVP table isconstrained such that the associated motion information of the currentblock is added to the last entry of the HMVP table as a new HMVPcandidate if and only if one of the following is true—(1) the size ofcurrent block is larger than or equal to the MER size or (2) the currentblock is located at a bottom-right corner of the current MER. Referringback to FIG. 3 , PU1, PU6, PU7, and PU9 are examples of blocks that areat the bottom right of an MER.

For example, if implementing the first condition, video encoder 200 andvideo decoder 300 may be configured to store a table of HMVPs; determinemotion information for a first block of the video data; add the motioninformation for the first block to the table of HMVPs in response todetermining that the first block is larger than or equal to a size forthe MER; and use the table of HMVPs to decode a second block of thevideo data. If implementing the second condition, video encoder 200 andvideo decoder 300 may be configured to store a table of HMVPs; determinemotion information for a first block of the video data; add the motioninformation for the first block to the table of HMVPs in response todetermining that the first block is located at a bottom-right corner ofa MER; and use the table of HMVPs to decode a second block of the videodata.

In some examples, the associated motion information of the current blockis added to the last entry of the table as a new HMVP candidate if andonly if one of the following is true:

-   -   3) cbWidth>=merSize and cbHeight>=merSize    -   4) floor(xCb/merSize)<floor ((xCb+cbWidth)/merSize) and        floor(yCb/merSize)<floor((yCb+cbHeight)/merSize),        where xCb and yCb are the coordinates of top-left sample in the        current block, cbWidth and cbHeight are the width and height of        the current block, and merSize is the size of MER. Floor(x) is        the operator to get the maximum integer value that is smaller or        equal to x. For example, video encoder 200 and video decoder 300        may be configured to determine if a value of an x-coordinate of        a top-left sample of the first block plus a width of the first        block divided by a size of the MER is greater than the value of        the x-coordinate of the top-left sample divided by the size of        the MER and determine if a value of a y-coordinate of a top-left        sample of the first block plus a height of the first block        divided by the size of the MER is greater than the value of the        y-coordinate of the top-left sample divided by the size of the        MER. Video encoder 200 and video decoder 300 may be configured        to add the motion information for the first block to the table        of HMVPs in response to determining that the value of an        x-coordinate of the top-left sample of the first block plus a        width of the first block divided by the size of the MER is        greater than the value of the x-coordinate of the top-left        sample divided by the size of the MER and in response to        determining that the value of the y-coordinate of the top-left        sample of the first block plus the height of the first block        divided by the size of the MER is greater than the value of the        y-coordinate of the top-left sample divided by the size of the        MER.

In another example, the associated motion information of the currentblock is added to the last entry of the table as a new HMVP candidate ifand only if one of the following is true:

-   -   3) cbWidth>=merSize and cbHeight>=merSize    -   4) floor(xCb/merSize)+1==floor ((xCb+cbWidth)/merSize) and        floor(yCb/merSize)+1==floor ((yCb+cbHeight)/merSize).

In some examples of this disclosure, a second HMVP table may bemaintained. When coding a current block that is inside a MER, the secondtable is used instead of the original table. And the second HMVP tableis not updated with the associated motion information of the currentblock. The original HMVP table is updated with the associated motioninformation of the current block. When coding a current block thatconsists one or more MER, the original table is used.

In some examples, a second HMVP table is maintained. When coding acurrent block that is inside a MER, the second table is used instead ofthe original table. And the second HMVP table is not updated with theassociated motion information of the current block. The original HMVPtable is updated with the associated motion information of a limitednumber of blocks located at some specific positions inside the MER. Insome examples, the original HMVP table is updated with the associatedmotion information of current block if the current block is located atthe bottom-right corner of the current MER. In some examples, theoriginal HMVP table is updated with the associated motion information ofa current block if the current block is located at the center of thecurrent MER. In some examples, the original HMVP table is updated withthe associated motion information of the current block if the currentblock is located at the top-left corner of the current MER.

FIG. 4 is a block diagram illustrating an example video encoder 200 thatmay perform the techniques of this disclosure. FIG. 4 is provided forpurposes of explanation and should not be considered limiting of thetechniques as broadly exemplified and described in this disclosure. Forpurposes of explanation, this disclosure describes video encoder 200according to the techniques of JEM, VVC (ITU-T H.266, underdevelopment), and HEVC (ITU-T H.265). However, the techniques of thisdisclosure may be performed by video encoding devices that areconfigured to other video coding standards.

In the example of FIG. 4 , video encoder 200 includes video data memory230, mode selection unit 202, residual generation unit 204, transformprocessing unit 206, quantization unit 208, inverse quantization unit210, inverse transform processing unit 212, reconstruction unit 214,filter unit 216, decoded picture buffer (DPB) 218, and entropy encodingunit 220. Any or all of video data memory 230, mode selection unit 202,residual generation unit 204, transform processing unit 206,quantization unit 208, inverse quantization unit 210, inverse transformprocessing unit 212, reconstruction unit 214, filter unit 216, DPB 218,and entropy encoding unit 220 may be implemented in one or moreprocessors or in processing circuitry. For instance, the units of videoencoder 200 may be implemented as one or more circuits or logic elementsas part of hardware circuitry, or as part of a processor, ASIC, of FPGA.Moreover, video encoder 200 may include additional or alternativeprocessors or processing circuitry to perform these and other functions.

Video data memory 230 may store video data to be encoded by thecomponents of video encoder 200. Video encoder 200 may receive the videodata stored in video data memory 230 from, for example, video source 104(FIG. 1 ). DPB 218 may act as a reference picture memory that storesreference video data for use in prediction of subsequent video data byvideo encoder 200. Video data memory 230 and DPB 218 may be formed byany of a variety of memory devices, such as dynamic random access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. Video datamemory 230 and DPB 218 may be provided by the same memory device orseparate memory devices. In various examples, video data memory 230 maybe on-chip with other components of video encoder 200, as illustrated,or off-chip relative to those components.

In this disclosure, reference to video data memory 230 should not beinterpreted as being limited to memory internal to video encoder 200,unless specifically described as such, or memory external to videoencoder 200, unless specifically described as such. Rather, reference tovideo data memory 230 should be understood as reference memory thatstores video data that video encoder 200 receives for encoding (e.g.,video data for a current block that is to be encoded). Memory 106 ofFIG. 1 may also provide temporary storage of outputs from the variousunits of video encoder 200.

The various units of FIG. 4 are illustrated to assist with understandingthe operations performed by video encoder 200. The units may beimplemented as fixed-function circuits, programmable circuits, or acombination thereof. Fixed-function circuits refer to circuits thatprovide particular functionality, and are preset on the operations thatcan be performed. Programmable circuits refer to circuits that can beprogrammed to perform various tasks, and provide flexible functionalityin the operations that can be performed. For instance, programmablecircuits may execute software or firmware that cause the programmablecircuits to operate in the manner defined by instructions of thesoftware or firmware. Fixed-function circuits may execute softwareinstructions (e.g., to receive parameters or output parameters), but thetypes of operations that the fixed-function circuits perform aregenerally immutable. In some examples, one or more of the units may bedistinct circuit blocks (fixed-function or programmable), and in someexamples, one or more of the units may be integrated circuits.

Video encoder 200 may include arithmetic logic units (ALUs), elementaryfunction units (EFUs), digital circuits, analog circuits, and/orprogrammable cores, formed from programmable circuits. In examples wherethe operations of video encoder 200 are performed using softwareexecuted by the programmable circuits, memory 106 (FIG. 1 ) may storethe instructions (e.g., object code) of the software that video encoder200 receives and executes, or another memory within video encoder 200(not shown) may store such instructions.

Video data memory 230 is configured to store received video data. Videoencoder 200 may retrieve a picture of the video data from video datamemory 230 and provide the video data to residual generation unit 204and mode selection unit 202. Video data in video data memory 230 may beraw video data that is to be encoded.

Mode selection unit 202 includes a motion estimation unit 222, motioncompensation unit 224, and an intra-prediction unit 226. Mode selectionunit 202 may include additional functional units to perform videoprediction in accordance with other prediction modes. As examples, modeselection unit 202 may include a palette unit, an intra-block copy unit(which may be part of motion estimation unit 222 and/or motioncompensation unit 224), an affine unit, a linear model (LM) unit, or thelike.

Mode selection unit 202 generally coordinates multiple encoding passesto test combinations of encoding parameters and resultingrate-distortion values for such combinations. The encoding parametersmay include partitioning of CTUs into CUs, prediction modes for the CUs,transform types for residual data of the CUs, quantization parametersfor residual data of the CUs, and so on. Mode selection unit 202 mayultimately select the combination of encoding parameters havingrate-distortion values that are better than the other testedcombinations.

Video encoder 200 may partition a picture retrieved from video datamemory 230 into a series of CTUs, and encapsulate one or more CTUswithin a slice. Mode selection unit 202 may partition a CTU of thepicture in accordance with a tree structure, such as the QTBT structureor the quad-tree structure of HEVC described above. As described above,video encoder 200 may form one or more CUs from partitioning a CTUaccording to the tree structure. Such a CU may also be referred togenerally as a “video block” or “block.”

In general, mode selection unit 202 also controls the components thereof(e.g., motion estimation unit 222, motion compensation unit 224, andintra-prediction unit 226) to generate a prediction block for a currentblock (e.g., a current CU, or in HEVC, the overlapping portion of a PUand a TU). For inter-prediction of a current block, motion estimationunit 222 may perform a motion search to identify one or more closelymatching reference blocks in one or more reference pictures (e.g., oneor more previously coded pictures stored in DPB 218). In particular,motion estimation unit 222 may calculate a value representative of howsimilar a potential reference block is to the current block, e.g.,according to sum of absolute difference (SAD), sum of squareddifferences (SSD), mean absolute difference (MAD), mean squareddifferences (MSD), or the like. Motion estimation unit 222 may generallyperform these calculations using sample-by-sample differences betweenthe current block and the reference block being considered. Motionestimation unit 222 may identify a reference block having a lowest valueresulting from these calculations, indicating a reference block thatmost closely matches the current block.

Motion estimation unit 222 may form one or more motion vectors (MVs)that defines the positions of the reference blocks in the referencepictures relative to the position of the current block in a currentpicture. Motion estimation unit 222 may then provide the motion vectorsto motion compensation unit 224. For example, for uni-directionalinter-prediction, motion estimation unit 222 may provide a single motionvector, whereas for bi-directional inter-prediction, motion estimationunit 222 may provide two motion vectors. Motion compensation unit 224may then generate a prediction block using the motion vectors. Forexample, motion compensation unit 224 may retrieve data of the referenceblock using the motion vector. As another example, if the motion vectorhas fractional sample precision, motion compensation unit 224 mayinterpolate values for the prediction block according to one or moreinterpolation filters. Moreover, for bi-directional inter-prediction,motion compensation unit 224 may retrieve data for two reference blocksidentified by respective motion vectors and combine the retrieved data,e.g., through sample-by-sample averaging or weighted averaging. Motionestimation unit 222 and motion compensation unit 224 may be configuredto code blocks using MERs as described above.

As another example, for intra-prediction, or intra-prediction coding,intra-prediction unit 226 may generate the prediction block from samplesneighboring the current block. For example, for directional modes,intra-prediction unit 226 may generally mathematically combine values ofneighboring samples and populate these calculated values in the defineddirection across the current block to produce the prediction block. Asanother example, for DC mode, intra-prediction unit 226 may calculate anaverage of the neighboring samples to the current block and generate theprediction block to include this resulting average for each sample ofthe prediction block.

Mode selection unit 202 provides the prediction block to residualgeneration unit 204. Residual generation unit 204 receives a raw,unencoded version of the current block from video data memory 230 andthe prediction block from mode selection unit 202. Residual generationunit 204 calculates sample-by-sample differences between the currentblock and the prediction block. The resulting sample-by-sampledifferences define a residual block for the current block. In someexamples, residual generation unit 204 may also determine differencesbetween sample values in the residual block to generate a residual blockusing residual differential pulse code modulation (RDPCM). In someexamples, residual generation unit 204 may be formed using one or moresubtractor circuits that perform binary subtraction.

In examples where mode selection unit 202 partitions CUs into PUs, eachPU may be associated with a luma prediction unit and correspondingchroma prediction units. Video encoder 200 and video decoder 300 maysupport PUs having various sizes. As indicated above, the size of a CUmay refer to the size of the luma coding block of the CU and the size ofa PU may refer to the size of a luma prediction unit of the PU. Assumingthat the size of a particular CU is 2N×2N, video encoder 200 may supportPU sizes of 2N×2N or N×N for intra prediction, and symmetric PU sizes of2N×2N, 2N×N, N×2N, N×N, or similar for inter prediction. Video encoder200 and video decoder 300 may also support asymmetric partitioning forPU sizes of 2N×nU, 2N×nD, nL×2N, and nR×2N for inter prediction.

In examples where mode selection unit 202 does not further partition aCU into PUs, each CU may be associated with a luma coding block andcorresponding chroma coding blocks. As above, the size of a CU may referto the size of the luma coding block of the CU. The video encoder 200and video decoder 300 may support CU sizes of 2N×2N, 2N×N, or N×2N.

For other video coding techniques such as an intra-block copy modecoding, an affine-mode coding, and linear model (LM) mode coding, as fewexamples, mode selection unit 202, via respective units associated withthe coding techniques, generates a prediction block for the currentblock being encoded. In some examples, such as palette mode coding, modeselection unit 202 may not generate a prediction block, and insteadgenerate syntax elements that indicate the manner in which toreconstruct the block based on a selected palette. In such modes, modeselection unit 202 may provide these syntax elements to entropy encodingunit 220 to be encoded.

As described above, residual generation unit 204 receives the video datafor the current block and the corresponding prediction block. Residualgeneration unit 204 then generates a residual block for the currentblock. To generate the residual block, residual generation unit 204calculates sample-by-sample differences between the prediction block andthe current block.

Transform processing unit 206 applies one or more transforms to theresidual block to generate a block of transform coefficients (referredto herein as a “transform coefficient block”). Transform processing unit206 may apply various transforms to a residual block to form thetransform coefficient block. For example, transform processing unit 206may apply a discrete cosine transform (DCT), a directional transform, aKarhunen-Loeve transform (KLT), or a conceptually similar transform to aresidual block. In some examples, transform processing unit 206 mayperform multiple transforms to a residual block, e.g., a primarytransform and a secondary transform, such as a rotational transform. Insome examples, transform processing unit 206 does not apply transformsto a residual block.

Quantization unit 208 may quantize the transform coefficients in atransform coefficient block, to produce a quantized transformcoefficient block. Quantization unit 208 may quantize transformcoefficients of a transform coefficient block according to aquantization parameter (QP) value associated with the current block.Video encoder 200 (e.g., via mode selection unit 202) may adjust thedegree of quantization applied to the transform coefficient blocksassociated with the current block by adjusting the QP value associatedwith the CU. Quantization may introduce loss of information, and thus,quantized transform coefficients may have lower precision than theoriginal transform coefficients produced by transform processing unit206.

Inverse quantization unit 210 and inverse transform processing unit 212may apply inverse quantization and inverse transforms to a quantizedtransform coefficient block, respectively, to reconstruct a residualblock from the transform coefficient block. Reconstruction unit 214 mayproduce a reconstructed block corresponding to the current block (albeitpotentially with some degree of distortion) based on the reconstructedresidual block and a prediction block generated by mode selection unit202. For example, reconstruction unit 214 may add samples of thereconstructed residual block to corresponding samples from theprediction block generated by mode selection unit 202 to produce thereconstructed block.

Filter unit 216 may perform one or more filter operations onreconstructed blocks. For example, filter unit 216 may performdeblocking operations to reduce blockiness artifacts along edges of CUs.Operations of filter unit 216 may be skipped, in some examples.

Video encoder 200 stores reconstructed blocks in DPB 218. For instance,in examples where operations of filter unit 216 are not needed,reconstruction unit 214 may store reconstructed blocks to DPB 218. Inexamples where operations of filter unit 216 are needed, filter unit 216may store the filtered reconstructed blocks to DPB 218. Motionestimation unit 222 and motion compensation unit 224 may retrieve areference picture from DPB 218, formed from the reconstructed (andpotentially filtered) blocks, to inter-predict blocks of subsequentlyencoded pictures. In addition, intra-prediction unit 226 may usereconstructed blocks in DPB 218 of a current picture to intra-predictother blocks in the current picture.

In general, entropy encoding unit 220 may entropy encode syntax elementsreceived from other functional components of video encoder 200. Forexample, entropy encoding unit 220 may entropy encode quantizedtransform coefficient blocks from quantization unit 208. As anotherexample, entropy encoding unit 220 may entropy encode prediction syntaxelements (e.g., motion information for inter-prediction or intra-modeinformation for intra-prediction) from mode selection unit 202. Entropyencoding unit 220 may perform one or more entropy encoding operations onthe syntax elements, which are another example of video data, togenerate entropy-encoded data. For example, entropy encoding unit 220may perform a context-adaptive variable length coding (CAVLC) operation,a CABAC operation, a variable-to-variable (V2V) length coding operation,a syntax-based context-adaptive binary arithmetic coding (SBAC)operation, a Probability Interval Partitioning Entropy (PIPE) codingoperation, an Exponential-Golomb encoding operation, or another type ofentropy encoding operation on the data. In some examples, entropyencoding unit 220 may operate in bypass mode where syntax elements arenot entropy encoded.

Video encoder 200 may output a bitstream that includes the entropyencoded syntax elements needed to reconstruct blocks of a slice orpicture. In particular, entropy encoding unit 220 may output thebitstream.

The operations described above are described with respect to a block.Such description should be understood as being operations for a lumacoding block and/or chroma coding blocks. As described above, in someexamples, the luma coding block and chroma coding blocks are luma andchroma components of a CU. In some examples, the luma coding block andthe chroma coding blocks are luma and chroma components of a PU.

In some examples, operations performed with respect to a luma codingblock need not be repeated for the chroma coding blocks. As one example,operations to identify a motion vector (MV) and reference picture for aluma coding block need not be repeated for identifying a MV andreference picture for the chroma blocks. Rather, the MV for the lumacoding block may be scaled to determine the MV for the chroma blocks,and the reference picture may be the same. As another example, theintra-prediction process may be the same for the luma coding block andthe chroma coding blocks.

Video encoder 200 represents an example of a device configured to encodevideo data including a memory configured to store video data, and one ormore processing units implemented in circuitry and configured to performthe techniques of this disclosure. For example, mode selection unit 202(e.g., motion estimation unit 222 and/or motion compensation unit 224)may store a table of HMVPs to be used when constructing merge candidatelists for blocks coded in merge mode. Mode selection unit 202 maydetermine motion information for a first block of the video data, addthe motion information for the first block to the table of HMVPs inresponse to determining that the first block is located at abottom-right corner of a MER, and use the table of HMVPs to decode asecond block of the video data. Mode selection unit 202 may, forexample, generate a merge candidate list for the second block using anentry from the table of HMVPs.

FIG. 5 is a block diagram illustrating an example video decoder 300 thatmay perform the techniques of this disclosure. FIG. 5 is provided forpurposes of explanation and is not limiting on the techniques as broadlyexemplified and described in this disclosure. For purposes ofexplanation, this disclosure describes video decoder 300 according tothe techniques of JEM, VVC (ITU-T H.266, under development), and HEVC(ITU-T H.265). However, the techniques of this disclosure may beperformed by video coding devices that are configured to other videocoding standards.

In the example of FIG. 5 , video decoder 300 includes coded picturebuffer (CPB) memory 320, entropy decoding unit 302, predictionprocessing unit 304, inverse quantization unit 306, inverse transformprocessing unit 308, reconstruction unit 310, filter unit 312, anddecoded picture buffer (DPB) 314. Any or all of CPB memory 320, entropydecoding unit 302, prediction processing unit 304, inverse quantizationunit 306, inverse transform processing unit 308, reconstruction unit310, filter unit 312, and DPB 314 may be implemented in one or moreprocessors or in processing circuitry. For instance, the units of videodecoder 300 may be implemented as one or more circuits or logic elementsas part of hardware circuitry, or as part of a processor, ASIC, of FPGA.Moreover, video decoder 300 may include additional or alternativeprocessors or processing circuitry to perform these and other functions.

Prediction processing unit 304 includes motion compensation unit 316 andintra-prediction unit 318. Prediction processing unit 304 may includeadditional units to perform prediction in accordance with otherprediction modes. As examples, prediction processing unit 304 mayinclude a palette unit, an intra-block copy unit (which may form part ofmotion compensation unit 316), an affine unit, a linear model (LM) unit,or the like. In other examples, video decoder 300 may include more,fewer, or different functional components.

CPB memory 320 may store video data, such as an encoded video bitstream,to be decoded by the components of video decoder 300. The video datastored in CPB memory 320 may be obtained, for example, fromcomputer-readable medium 110 (FIG. 1 ). CPB memory 320 may include a CPBthat stores encoded video data (e.g., syntax elements) from an encodedvideo bitstream. Also, CPB memory 320 may store video data other thansyntax elements of a coded picture, such as temporary data representingoutputs from the various units of video decoder 300. DPB 314 generallystores decoded pictures, which video decoder 300 may output and/or useas reference video data when decoding subsequent data or pictures of theencoded video bitstream. CPB memory 320 and DPB 314 may be formed by anyof a variety of memory devices, such as DRAM, including SDRAM, MRAM,RRAM, or other types of memory devices. CPB memory 320 and DPB 314 maybe provided by the same memory device or separate memory devices. Invarious examples, CPB memory 320 may be on-chip with other components ofvideo decoder 300, or off-chip relative to those components.

Additionally or alternatively, in some examples, video decoder 300 mayretrieve coded video data from memory 120 (FIG. 1 ). That is, memory 120may store data as discussed above with CPB memory 320. Likewise, memory120 may store instructions to be executed by video decoder 300, whensome or all of the functionality of video decoder 300 is implemented insoftware to be executed by processing circuitry of video decoder 300.

The various units shown in FIG. 5 are illustrated to assist withunderstanding the operations performed by video decoder 300. The unitsmay be implemented as fixed-function circuits, programmable circuits, ora combination thereof. Similar to FIG. 4 , fixed-function circuits referto circuits that provide particular functionality, and are preset on theoperations that can be performed. Programmable circuits refer tocircuits that can be programmed to perform various tasks, and provideflexible functionality in the operations that can be performed. Forinstance, programmable circuits may execute software or firmware thatcause the programmable circuits to operate in the manner defined byinstructions of the software or firmware. Fixed-function circuits mayexecute software instructions (e.g., to receive parameters or outputparameters), but the types of operations that the fixed-functioncircuits perform are generally immutable. In some examples, one or moreof the units may be distinct circuit blocks (fixed-function orprogrammable), and in some examples, one or more of the units may beintegrated circuits.

Video decoder 300 may include ALUs, EFUs, digital circuits, analogcircuits, and/or programmable cores formed from programmable circuits.In examples where the operations of video decoder 300 are performed bysoftware executing on the programmable circuits, on-chip or off-chipmemory may store instructions (e.g., object code) of the software thatvideo decoder 300 receives and executes.

Entropy decoding unit 302 may receive encoded video data from the CPBand entropy decode the video data to reproduce syntax elements.Prediction processing unit 304, inverse quantization unit 306, inversetransform processing unit 308, reconstruction unit 310, and filter unit312 may generate decoded video data based on the syntax elementsextracted from the bitstream.

In general, video decoder 300 reconstructs a picture on a block-by-blockbasis. Video decoder 300 may perform a reconstruction operation on eachblock individually (where the block currently being reconstructed, i.e.,decoded, may be referred to as a “current block”).

Entropy decoding unit 302 may entropy decode syntax elements definingquantized transform coefficients of a quantized transform coefficientblock, as well as transform information, such as a quantizationparameter (QP) and/or transform mode indication(s). Inverse quantizationunit 306 may use the QP associated with the quantized transformcoefficient block to determine a degree of quantization and, likewise, adegree of inverse quantization for inverse quantization unit 306 toapply. Inverse quantization unit 306 may, for example, perform a bitwiseleft-shift operation to inverse quantize the quantized transformcoefficients. Inverse quantization unit 306 may thereby form a transformcoefficient block including transform coefficients.

After inverse quantization unit 306 forms the transform coefficientblock, inverse transform processing unit 308 may apply one or moreinverse transforms to the transform coefficient block to generate aresidual block associated with the current block. For example, inversetransform processing unit 308 may apply an inverse DCT, an inverseinteger transform, an inverse Karhunen-Loeve transform (KLT), an inverserotational transform, an inverse directional transform, or anotherinverse transform to the transform coefficient block.

Furthermore, prediction processing unit 304 generates a prediction blockaccording to prediction information syntax elements that were entropydecoded by entropy decoding unit 302. For example, if the predictioninformation syntax elements indicate that the current block isinter-predicted, motion compensation unit 316 may generate theprediction block. In this case, the prediction information syntaxelements may indicate a reference picture in DPB 314 from which toretrieve a reference block, as well as a motion vector identifying alocation of the reference block in the reference picture relative to thelocation of the current block in the current picture. Motioncompensation unit 316 may generally perform the inter-prediction processin a manner that is substantially similar to that described with respectto motion compensation unit 224 (FIG. 4 ). Motion compensation unit 316may be configured to decode blocks using MERs as described above.

As another example, if the prediction information syntax elementsindicate that the current block is intra-predicted, intra-predictionunit 318 may generate the prediction block according to anintra-prediction mode indicated by the prediction information syntaxelements. Again, intra-prediction unit 318 may generally perform theintra-prediction process in a manner that is substantially similar tothat described with respect to intra-prediction unit 226 (FIG. 4 ).Intra-prediction unit 318 may retrieve data of neighboring samples tothe current block from DPB 314.

Reconstruction unit 310 may reconstruct the current block using theprediction block and the residual block. For example, reconstructionunit 310 may add samples of the residual block to corresponding samplesof the prediction block to reconstruct the current block.

Filter unit 312 may perform one or more filter operations onreconstructed blocks. For example, filter unit 312 may performdeblocking operations to reduce blockiness artifacts along edges of thereconstructed blocks. Operations of filter unit 312 are not necessarilyperformed in all examples.

Video decoder 300 may store the reconstructed blocks in DPB 314. Forinstance, in examples where operations of filter unit 312 are notperformed, reconstruction unit 310 may store reconstructed blocks to DPB314. In examples where operations of filter unit 312 are performed,filter unit 312 may store the filtered reconstructed blocks to DPB 314.As discussed above, DPB 314 may provide reference information, such assamples of a current picture for intra-prediction and previously decodedpictures for subsequent motion compensation, to prediction processingunit 304. Moreover, video decoder 300 may output decoded pictures (e.g.,decoded video) from DPB 314 for subsequent presentation on a displaydevice, such as display device 118 of FIG. 1 .

Video decoder 300 represents an example of a device configured to decodevideo data including a memory configured to store video data, and one ormore processing units implemented in circuitry and configured to performthe techniques of this disclosure. For example, prediction processingunit 304 (e.g., motion compensation unit 316) may store a table of HMVPsto be used when constructing merge candidate lists for blocks coded inmerge mode. Prediction processing unit 304 may determine motioninformation for a first block of the video data, add the motioninformation for the first block to the table of HMVPs in response todetermining that the first block is located at a bottom-right corner ofa MER, and use the table of HMVPs to decode a second block of the videodata. prediction processing unit 304 may, for example, generate a mergecandidate list for the second block using an entry from the table ofHMVPs.

FIG. 6 is a flowchart illustrating an example process for encoding acurrent block. The current block may comprise a current CU. Althoughdescribed with respect to video encoder 200 (FIGS. 1 and 4 ), it shouldbe understood that other devices may be configured to perform a processsimilar to that of FIG. 6 .

In this example, video encoder 200 initially predicts the current block(350). As part of predicting the block, video encoder 200 may maintainone or more HMVP tables as disclosed herein and may update those tablesaccording to the techniques described herein. For example, video encoder200 may form a prediction block for the current block. Video encoder 200may then calculate a residual block for the current block (352). Tocalculate the residual block, video encoder 200 may calculate adifference between the original, unencoded block and the predictionblock for the current block. Video encoder 200 may then transform theresidual block and quantize transform coefficients of the residual block(354). Next, video encoder 200 may scan the quantized transformcoefficients of the residual block (356). During the scan, or followingthe scan, video encoder 200 may entropy encode the transformcoefficients (358). For example, video encoder 200 may encode thetransform coefficients using CAVLC or CABAC. Video encoder 200 may thenoutput the entropy encoded data of the block (360).

FIG. 7 is a flowchart illustrating an example process for decoding acurrent block of video data. The current block may comprise a currentCU. Although described with respect to video decoder 300 (FIGS. 1 and 5), it should be understood that other devices may be configured toperform a process similar to that of FIG. 7 .

Video decoder 300 may receive entropy encoded data for the currentblock, such as entropy encoded prediction information and entropyencoded data for coefficients of a residual block corresponding to thecurrent block (370). Video decoder 300 may entropy decode the entropyencoded data to determine prediction information for the current blockand to reproduce coefficients of the residual block (372). Video decoder300 may predict the current block (374), e.g., using an intra- orinter-prediction mode as indicated by the prediction information for thecurrent block, to calculate a prediction block for the current block. Aspart of predicting the block, video decoder 300 may maintain one or moreHMVP tables as disclosed herein and may update those tables according tothe techniques described herein. Video decoder 300 may then inverse scanthe reproduced coefficients (376), to create a block of quantizedtransform coefficients. Video decoder 300 may then inverse quantize andinverse transform the transform coefficients to produce a residual block(378). Video decoder 300 may ultimately decode the current block bycombining the prediction block and the residual block (380).

FIG. 8 is a flowchart illustrating an example process for decoding acurrent block of video data. The current block may comprise a currentCU. The techniques of FIG. 8 will be described with respect to a genericvideo decoder, which may, for example, correspond to video decoder 300(FIGS. 1 and 5 ), the video decoding loop of video encoder 200 (FIGS. 1and 4 ), or any other such video decoder.

The video decoder stores a table of HMVPs (400). The video decoder may,for example, maintain a table of HMVPs, and as new blocks are decoded,the video decoder may add the motion information used to decode the newblocks to the table of HMVPs. The decoder may also periodically removeentries from the table of HMVPs, so as to limit the size of the table.The video decoder determines motion information for a first block of thevideo data (402). The video decoder may, for example, use the determinedmotion information to inter predict the first block.

The video decoder adds the motion information for the first block to thetable of HMVPs in response to determining that the first block islocated at a bottom-right corner of a MER (404). The MER may be a firstMER, and the second block may belong to a second MER. To add the motioninformation for the first block to the table of HMVPs in response todetermining that the first block is located at the bottom-right cornerof the MER, the video decoder may for example, determine if a value ofan x-coordinate of a top-left sample of the first block plus a width ofthe first block divided by a size of the MER is greater than the valueof the x-coordinate of the top-left sample divided by the size of theMER and determine if a value of a y-coordinate of a top-left sample ofthe first block plus a height of the first block divided by the size ofthe MER is greater than the value of the y-coordinate of the top-leftsample divided by the size of the MER. In response to determining thatthe value of an x-coordinate of the top-left sample of the first blockplus a width of the first block divided by the size of the MER isgreater than the value of the x-coordinate of the top-left sampledivided by the size of the MER and in response to determining that thevalue of the y-coordinate of the top-left sample of the first block plusthe height of the first block divided by the size of the MER is greaterthan the value of the y-coordinate of the top-left sample divided by thesize of the MER, the video decoder may add the motion information forthe first block to the table of HMVPs.

The video decoder uses the table of HMVPs to decode a second block ofthe video data (406). To use the table of HMVPs to decode the secondblock of the video data, the video decoder may, for example, beconfigured to generate a candidate list of motion information for thesecond block that includes a candidate from the table of HMVPs; select acandidate from the candidate list of motion vectors; and use theselected candidate to decode the second block of video data. The videodecoder may, for example, output decoded video data that includesdecoded versions of the first block and the second block. Inimplementations where the video decoder is operating to perform a videoencoding process, the video decoder may store one or more decodedpicture that include decoded versions of the first block and the secondblock and use the one or more stored decoded pictures to encode otherblocks of other pictures of the video data.

The following clauses represents example implementations of thetechniques and devices introduced above.

Clause 1: A method of coding video data includes storing a table ofhistory-based motion vector predictors (HMVPs); determining motioninformation for a current block of video data; and updating the table ofhistory-based motion vector predictors based on the determined motioninformation for the current block according to any technique orcombination of techniques described in this disclosure.

Clause 2: The method of clause 1, wherein updating the table of HMVPsbased on the determined motion information for the current blockcomprises: adding the motion information for the current block to thetable of HMVPs in response to determining that the current block islarger than or equal to a size for a motion estimation region.

Clause 3: The method of clause 1, wherein updating the table of HMVPsbased on the determined motion information for the current blockcomprises: adding the motion information for the current block to thetable of HMVPs in response to determining that the current block islocated at a bottom-right corner of a motion estimation region.

Clause 4: The method of any of clauses 1-3, further includes for asecond current block being coded after the current block, generating acandidate list for the second current block by adding a candidate fromthe table of HMVPs to the candidate list.

Clause 5: A method of coding video data includes storing a first tableof history-based motion vector predictors (HMVPs); storing a secondtable of HMVPs; determining motion information for a current block ofvideo data; and updating the first table of HMVPs and/or the secondtable of HMVPs based on the determined motion information for thecurrent block according to any technique or combination of techniquesdescribed in this disclosure.

Clause 6: The method of clause 5, further includes for a second currentblock being coded after the current block, generating a candidate listfor the second current block by adding a candidate from the first tableof HMVPs or the second table of HMVPs to the candidate list.

Clause 7: The method of any of clauses 1-6, wherein coding comprisesdecoding.

Clause 8: The method of any of clauses 1-6, wherein coding comprisesencoding.

Clause 9: A device for coding video data, the device comprising one ormore means for performing the method of any of clauses 1-8.

Clause 10: The device of clause 9, wherein the one or more meanscomprise one or more processors implemented in circuitry.

Clause 11: The device of any of clauses 9 and 10, further comprising amemory to store the video data.

Clause 12: The device of any of clauses 9-11, further comprising adisplay configured to display decoded video data.

Clause 13: The device of any of clauses 9-12, wherein the devicecomprises one or more of a camera, a computer, a mobile device, abroadcast receiver device, or a set-top box.

Clause 14: The device of any of clauses 9-13, wherein the devicecomprises a video decoder.

Clause 15: The device of any of clauses 9-14, wherein the devicecomprises a video encoder.

Clause 16: A computer-readable storage medium having stored thereoninstructions that, when executed, cause one or more processors toperform the method of any of clauses 1-8.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore DSPs, general purpose microprocessors, application specificintegrated circuits ASICs, FPGAs, or other equivalent integrated ordiscrete logic circuitry. Accordingly, the terms “processor” and“processing circuitry,” as used herein may refer to any of the foregoingstructures or any other structure suitable for implementation of thetechniques described herein. In addition, in some aspects, thefunctionality described herein may be provided within dedicated hardwareand/or software modules configured for encoding and decoding, orincorporated in a combined codec. Also, the techniques could be fullyimplemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of decoding video data, the methodcomprising: (a) storing a table of history-based motion vectorpredictors (HMVPs); (b) determining motion information for a first blockof the video data; (c) determining that the first block is located at abottom-right corner of a motion estimation region (MER); (d) determiningif a value of (an x-coordinate of a top-left sample of the first blockplus a width of the first block divided by a size of the MER) is greaterthan (the value of the x-coordinate of the top-left sample divided bythe size of the MER); (e) determining if a value of (a y-coordinate of atop-left sample of the first block plus a height of the first blockdivided by the size of the MER) is greater than (the value of they-coordinate of the top-left sample divided by the size of the MER);adding the motion information for the first block to the table of HMVPsin response to (c), (d) and (e) being true; and using the table of HMVPsto decode a second block of the video data.
 2. The method of claim 1,wherein using the table of HMVPs to decode the second block of the videodata comprises: for the second block, generating a candidate list ofmotion information, wherein the candidate list includes a candidate fromthe table of HMVPs; selecting a candidate from the candidate list ofmotion vectors; and using the selected candidate to decode the secondblock of video data.
 3. The method of claim 1, wherein the MER is afirst MER, and wherein the second block belongs to a second MER.
 4. Themethod of claim 1, wherein the determining if a value of (anx-coordinate of a top-left sample of the first block plus a width of thefirst block divided by a size of the MER) is greater (the value of thex-coordinate of the top-left sample divided by the size of the MER) isrepresented asfloor(xCb/merSize)<floor((xCb+cbWidth)/merSize), wherein the determiningif a value of (a y-coordinate of a top-left sample of the first blockplus a height of the first block divided by the size of the MER) isgreater than (the value of the y-coordinate of the top-left sampledivided by the size of the MER) is represented asfloor(yCb/merSize)<floor((yCb+cbHeight)/merSize), wherein the xCbrepresents the x-coordinate of the top-left sample of the first block,the yCb represents the y-coordinate of the top-left sample of the firstblock, the cbWidth represents the width of the first block, the cbHeightrepresents the height of the first block, the merSize represents thesize of the MER, < represents a less than operation, and the floor( )represents a floor operation.
 5. The method of claim 1, furthercomprising: outputting decoded video data that includes decoded versionsof the first block and the second block.
 6. The method of claim 1,wherein the method of decoding is performed as part of a video encodingprocess, the method further comprising: storing one or more decodedpicture that include decoded versions of the first block and the secondblock; and using the one or more stored decoded pictures to encode otherblocks of other pictures of the video data.
 7. A device for decodingvideo data, the device comprising: a memory configured to store videodata; and one or more processors implemented in circuitry and configuredto: (a) store a table of history-based motion vector predictors (HMVPs);(b) determine motion information for a first block of the video data;(c) determine that the first block is located at a bottom-right cornerof a motion estimation region (MER); (d) determine if a value of (anx-coordinate of a top-left sample of the first block plus a width of thefirst block divided by a size of the MER) is greater than (the value ofthe x-coordinate of the top-left sample divided by the size of the MER);(e) determine if a value of (a y-coordinate of a top-left sample of thefirst block plus a height of the first block divided by the size of theMER) is greater than (the value of the y-coordinate of the top-leftsample divided by the size of the MER); add the motion information forthe first block to the table of HMVPs in response to (c), (d) and (e)being true; and use the table of HMVPs to decode a second block of thevideo data.
 8. The device of claim 7, wherein to use the table of HMVPsto decode the second block of the video data, the one or more processorsare further configured to: for the second block, generate a candidatelist of motion information, wherein the candidate list includes acandidate from the table of HMVPs; select a candidate from the candidatelist of motion vectors; and use the selected candidate to decode thesecond block of video data.
 9. The device of claim 7, wherein the MER isa first MER, and wherein the second block belongs to a second MER. 10.The device of claim 7, wherein the determine if a value of (anx-coordinate of a top-left sample of the first block plus a width of thefirst block divided by a size of the MER) is greater (the value of thex-coordinate of the top-left sample divided by the size of the MER) isrepresented asfloor(xCb/merSize)<floor((xCb+cbWidth)/merSize), wherein the determineif a value of (a y-coordinate of a top-left sample of the first blockplus a height of the first block divided by the size of the MER) isgreater than (the value of the y-coordinate of the top-left sampledivided by the size of the MER) is represented asfloor(yCb/merSize)<floor((yCb+cbHeight)/merSize), wherein the xCbrepresents the x-coordinate of the top-left sample of the first block,the yCb represents the y-coordinate of the top-left sample of the firstblock, the cbWidth represents the width of the first block, the cbHeightrepresents the height of the first block, the merSize represents thesize of the MER, < represents a less than operation, and the floor( )represents a floor operation.
 11. The device of claim 7, wherein the oneor more processors are further configured to: output decoded video datathat includes decoded versions of the first block and the second block.12. The device of claim 7, wherein the device comprise a video encoderand wherein the one or more processors are further configured to: storeone or more decoded picture that include decoded versions of the firstblock and the second block; and use the one or more stored decodedpictures to encode other blocks of other pictures of the video data. 13.The device of claim 7, wherein the device comprises a wirelesscommunication device, further comprising a receiver configured toreceive encoded video data.
 14. The device of claim 13, wherein thewireless communication device comprises a telephone handset and whereinthe receiver is configured to demodulate, according to a wirelesscommunication standard, a signal comprising the encoded video data. 15.The device of claim 7, further comprising: a display configured todisplay decoded video data.
 16. The device of claim 7, wherein thedevice comprises one or more of a camera, a computer, a mobile device, abroadcast receiver device, or a set-top box.
 17. The device of claim 7,wherein the device comprises a wireless communication device, furthercomprising a transmitter configured to transmit encoded video data. 18.The device of claim 17, wherein the wireless communication devicecomprises a telephone handset and wherein the transmitter is configuredto modulate, according to a wireless communication standard, a signalcomprising the encoded video data.
 19. The device of claim 7, furthercomprising: a camera configured to capture the video data.
 20. Acomputer-readable storage medium storing instructions that when executedby one or more processors cause the one or more processors to: (a) storea table of history-based motion vector predictors (HMVPs); (b) determinemotion information for a first block of the video data; (c) determinethat the first block is located at a bottom-right corner of a motionestimation region (MER); (d) determine if a value of (an x-coordinate ofa top-left sample of the first block plus a width of the first blockdivided by a size of the MER) is greater than (the value of thex-coordinate of the top-left sample divided by the size of the MER); (e)determine if a value of (a y-coordinate of a top-left sample of thefirst block plus a height of the first block divided by the size of theMER) is greater than (the value of the y-coordinate of the top-leftsample divided by the size of the MER); add the motion information forthe first block to the table of HMVPs in response to (c), (d) and (e)being true; and use the table of HMVPs to decode a second block of thevideo data.
 21. The computer-readable storage medium of claim 20,wherein to use the table of HMVPs to decode the second block of thevideo data, the instruction cause the one or more processors to: for thesecond block, generate a candidate list of motion information, whereinthe candidate list includes a candidate from the table of HMVPs; selecta candidate from the candidate list of motion vectors; and use theselected candidate to decode the second block of video data.
 22. Thecomputer-readable storage medium of claim 20, wherein the MER is a firstMER, and wherein the second block belongs to a second MER.
 23. Thecomputer-readable storage medium of claim 20, wherein the determine if avalue of (an x-coordinate of a top-left sample of the first block plus awidth of the first block divided by a size of the MER) is greater (thevalue of the x-coordinate of the top-left sample divided by the size ofthe MER) is represented asfloor(xCb/merSize)<floor((xCb+cbWidth)/merSize), wherein the determineif a value of (a y-coordinate of a top-left sample of the first blockplus a height of the first block divided by the size of the MER) isgreater than (the value of the y-coordinate of the top-left sampledivided by the size of the MER) is represented asfloor(yCb/merSize)<floor((yCb+cbHeight)/merSize), wherein the xCbrepresents the x-coordinate of the top-left sample of the first block,the yCb represents the y-coordinate of the top-left sample of the firstblock, the cbWidth represents the width of the first block, the cbHeightrepresents the height of the first block, the merSize represents thesize of the MER, < represents a less than operation, and the floor( )represents a floor operation.